### Abstract

We investigate the change in the multiplicities of the eigenvalues of a Hermitian matrix with a simple graph G, when edges are inserted into G or removed from G. We focus upon cases in which the multiplicity of the eigenvalue does not change due to inserting or removing edges incident to a vertex. Furthermore, we show how the change in the multiplicities of the eigenvalues occur, when two disjoint graphs are connected with one edge, based upon the status of the vertices that are connected. Lastly, we give the possible classifications of cut-edges in a graph and characterize the occurrence of each possible status.

Original language | English |
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Pages (from-to) | 86-99 |

Number of pages | 14 |

Journal | Linear Algebra and Its Applications |

Volume | 560 |

DOIs | |

Publication status | Published - 1 Jan 2019 |

### Keywords

- Cut-edge
- Edge
- Eigenvalues
- Graph
- Hermitian matrix
- Multiplicity

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## Cite this

Johnson, C. R., Saiago, C. M., & Toyonaga, K. (2019). The change in multiplicity of an eigenvalue due to adding or removing edges.

*Linear Algebra and Its Applications*,*560*, 86-99. https://doi.org/10.1016/j.laa.2018.09.017